The 72nd 24 Hours of Le Mans (French: 72e 24 Heures du Mans) was an automobile endurance racing event held from 12 to 13 June at the Circuit de la Sarthe at Le Mans, France. It was the 72nd edition of the 24 Hour race, as organised by the automotive group, the Automobile Club de l'Ouest (ACO) since 1923. Unlike other events, it was not a part of any endurance motor racing championship. A test day was held eight weeks prior to the race on 25 April. Approximately 200,000 people attended the race.
The No. 88 Audi Sport UK Team Veloqx R8 of Jamie Davies, Johnny Herbert and Guy Smith started from pole position after Herbert set the overall fastest lap time in the fourth qualifying session. The car led for much of the first eighteen hours until a rear suspension problem created handling difficulties and was corrected in the garage. It gave the lead to the No. 5 Audi Sport Japan Team Goh car of Seiji Ara, Rinaldo Capello and Tom Kristensen and although it caught fire during a pit stop, Ara held off a challenge from the faster Herbert for the rest of the race to win by 41.354 seconds. It was Ara's first Le Mans win, Capello's second and Kristensen's sixth. Kristensen equalled Jacky Ickx's all-time record of six overall victories and was the first driver to win the 24 hour race five times in a row. This was the fourth overall victory for Audi since the manufacturer's début at the 2000 edition. The No. 88 Audi Sport UK Team Veloqx car finished in second and the No. 2 Champion Racing Audi R8 of JJ Lehto, Emanuele Pirro and Marco Werner recovered from a crash in the second hour to complete the overall podium finishers in third place.
The 2004 24 Hours of Le Mans was the 72nd edition of the race and took place at the 8.482 mi (13.650 km) Circuit de la Sarthe from 12 to 13 June. The race was conceived at the 1922 Paris Motor Show by the automotive journalist Charles Faroux, Georges Durand, the president of the automotive group, the Automobile Club de l'Ouest (ACO) and the industrialist Emile Coquile as a means of prompting car manufacturers to test the reliability and fuel-efficiency of their racing vehicles and equipment. It was not held in 1936 because of a general labour strike during the Great Depression, and heavy damage sustained to the circuit in World War II cancelled it from 1940 to 1948. The 24 Hours of Le Mans is considered one of the world's most prestigious motor races and is part of the Triple Crown of Motorsport.
In March 2003, the ACO announced changes to the Le Mans Prototype (LMP) classes that took effect from the 2004 race. The former Le Mans Grand Touring Prototype and Le Mans Prototype 900 (LMP900) categories merged and was renamed Le Mans Prototype 1 (LMP1) and was limited solely to manufacturers. The Le Mans Prototype 675 (LMP675) category had no car capable of challenging for the overall victory and the ACO designated it a lower class and renamed it Le Mans Prototype 2 (LMP2). LMP900 and LMP675 cars built in compliance with the ACO technical regulations for the LMP and LMGTP categories could enter until 31 December 2005. Skid blocks were made 10 mm (0.39 in) thicker and the air restrictor size was reduced by five per cent. Teams in LMP1 and LMP2 could choose between an open or a closed cockpit. The maximum weight of LMP2 vehicles was established at 750 kg (1,650 lb) and 900 kg (2,000 lb) for LMP1 cars. Engine displacement for normally aspirated engines set at 3,400 cc (210 cu in), turbocharged engines were limited to 2,000 cc (120 cu in) and engine displacement for diesel power units was restricted to 5,500 cc (340 cu in).
After a series of airborne accidents in sports car racing, such as a Porsche 911 GT1 at the 1998 Petit Le Mans and the Mercedes-Benz CLR at the 1999 Le Mans race, the ACO altered the bottom of the LMP1 and LMP2 cars to lower the amount of downforce produced outside of its wheelbase and a reduction in rear overhang coupled an increase in front overhang for less pitch sensitivity to minimise the possibility of such a crash occurring. The rear wing was moved forward and shortened from 400 mm (40 cm) to 300 mm (30 cm). A 20 mm (2.0 cm) plank was added to the underside of all LMP cars to force an increase in ride height and reduce the effectiveness of underfloor aerodynamics.